Segmented copolymer compositions and coatings incorporating these compositions

ABSTRACT

Some variations provide a segmented copolymer composition comprising: fluoropolymer first soft segments that are (α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated; polyester or polyether second soft segments that are (α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated; isocyanate species possessing an isocyanate functionality of 2 or greater; and polyol or polyamine chain extenders or crosslinkers, wherein the molar ratio of the second soft segments to the first soft segments is less than 2.0. Exemplary segmented copolymers are disclosed. The segmented copolymer composition may be present in a low-friction, low-adhesion coating. Such a coating may be characterized by a coefficient of friction, measured at 90% relative humidity, less than 0.7. Such a coating may be characterized by an average kinetic delay of surface ice formation of at least 10 minutes at −10° C. These coatings are useful as bugphobic and icephobic coatings.

PRIORITY DATA

This patent application is a divisional application of U.S. Pat. No.10,125,227, issued on Nov. 13, 2018, which claims priority to U.S.Provisional Patent App. No. 62/038,878, filed on Aug. 19, 2014, andwhich is a continuation-in-part of U.S. Pat. No. 10,344,244, issued onJul. 9, 2019, each of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to low-friction and low-adhesionmaterials, coatings, and systems.

BACKGROUND OF THE INVENTION

Coatings and materials can become soiled from debris (particles,insects, oils, etc.) impacting the surface. The debris affects airflowover the surface as well as aesthetics and normally is removed bywashing.

Many attempts are described to mitigate insect accumulation during theearly days of aircraft development. These include mechanical scrapers,deflectors, traps, in-flight detachable surfaces, in-flight dissolvablesurfaces, viscous surface fluids, continuous washing fluids, and suctionslots. The results of most of these trials were determined ineffectiveor impractical for commercial use.

Recently, Wohl et al., “Evaluation of commercially available materialsto mitigate insect residue adhesion on wing leading edge surfaces,”Progress in Organic Coatings 76 (2013) 42-50 describe work at NASA tocreate anti-insect adhesion or “bugphobic” surfaces. Wohl et al. testedthe effect of organic-based coatings on insect adhesion to surfaces, butthe coatings did not fully mitigate the issue. Wohl et al. also describepreviously used approaches to reduce bug adhesion such as mechanicalscrapers, deflectors, paper and/or other coverings, elastic surfaces,soluble films, and washing the surface continually with fluid.

One approach to this problem is to create a self-cleaning surface thatremoves debris from itself by controlling chemical interactions betweenthe debris and the surface.

Superhydrophobic and superoleophobic surfaces create very high contactangles)(>150° between the surface and drops of water and oil,respectively. The high contact angles result in the drops rolling offthe surface rather than remaining on the surface. These surfaces do notrepel solid foreign matter or vapors of contaminants. Once soiled byimpact, debris will remain on the surface and render it ineffective.Also, these surfaces lose function if the nanostructured top surface isscratched.

Enzyme-filled coatings leech out enzymes that dissolve debris on thesurface. However, the enzymes are quickly depleted and cannot berefilled, rendering this approach impractical.

Kok et al., “Influence of surface characteristics on insect residueadhesion to aircraft leading edge surfaces,” Progress in OrganicCoatings 76 (2013) 1567-1575, describe various polymer, sol-gel, andsuperhydrophobic coatings tested for reduced insect adhesion afterimpact. The best-performing materials were high-roughness,superhydrophobic surfaces. However, they did not show that debris couldbe removed from the superhydrophobic surfaces once insects broke on thesurface.

Polymeric materials having low surface energies are widely used fornon-stick coatings. These materials are tailored with careful control oftheir chemical composition (thus surface energy) and mechanicalproperties. Polymers containing low-energy perfluoropolyethers andperfluoroalkyl groups have been explored for low adhesion and solventrepellency applications. While these low-energy polymers facilitaterelease of materials adhering to them in both air and water, they do notnecessarily prevent adhesion of foreign substances. See Vaidya andChaudhury, “Synthesis and Surface Properties of EnvironmentallyResponsive Segmented Polyurethanes,” Journal of Colloid and InterfaceScience 249, 235-245 (2002). A fluorinated polyurethane is described inU.S. Pat. No. 5,332,798 issued Jul. 26, 1994 to Ferreri et al.

Fluoropolymer sheets or treated surfaces have low surface energies andthus low adhesion force between foreign matter and the surface. However,friction between impacting debris and the surface results in thesticking of contaminants.

Fluorofluid-filled surfaces have very low adhesion between impactingdebris and the surface. However, if any of the fluid is lost, thesurface cannot be refilled/renewed once applied on the vehicle, and thusloses its properties (see Wong et al., “Bioinspired self-repairingslippery surfaces with pressure-stable omniphobicity,” Nature 477,443-447, 2011).

In view of the shortcomings in the art, improved coating materials andmaterial systems, and compositions suitable for these systems, areneeded. Improved properties with respect to freezing delays andcoefficients of friction are desired.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs in the art, aswill now be summarized and then further described in detail below.

Some variations provide a segmented copolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0.

In some embodiments, the molar ratio of the second soft segments to thefirst soft segments is from about 0.1 to about 1.5.

In some embodiments, the fluoropolymers are selected from the groupconsisting of polyfluoroethers, perfluoropolyethers,polyfluoroacrylates, polyfluorosiloxanes, and combinations thereof. Incertain embodiments, the fluoropolymers include a fluoropolymer havingthe structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol) (also known as poly(propylene oxide)),poly(tetrahydrofuran), poly(glycolic acid), poly(caprolactone),poly(ethylene adipate), poly(hydroxybutyrate), poly(hydroxyalkanoate),and combinations thereof.

In some embodiments, the isocyanate species is selected from the groupconsisting of 4,4′-methylenebis(cyclohexyl isocyanate), hexamethylenediisocyanate, cycloalkyl-based diisocyanates, tolylene-2,4-diisocyanate,4,4′-methylenebis(phenyl isocyanate), isophorone diisocyanate, andcombinations or derivatives thereof.

The polyol or polyamine chain extender or crosslinker possesses afunctionality of 2 or greater, in some embodiments. At least one polyolor polyamine chain extender or crosslinker may be selected from thegroup consisting of 1,3-butanediol,1,4-butanediol, 1,3-propanediol,1,2-ethanediol, diethylene glycol, triethylene glycol, tetraethyleneglycol, propylene glycol, dipropylene glycol, tripropylene glycol,neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, ethanolamine, diethanol amine, methyldiethanolamine, phenyldiethanolamine,glycerol, trimethylolpropane, 1,2,6-hexanetriol, triethanolamine,pentaerythritol, ethylenediamine, 1,3-propanediamine, 1,4-buatendiamine,diethyltoluenediamine, dimethylthiotoluenediamine, isophoronediamine,diaminocyclohexane, N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine,and homologues, derivatives, or combinations thereof.

Following a suitable chemical reaction, the segmented copolymercomposition contains, in a hard segment, the reacted form of the one ormore isocyanate species, combined with the reacted form of the one ormore polyol or polyamine chain extenders or crosslinkers. In someembodiments, the hard segment is present in an amount from about 5 wt %to about 60 wt %, based on total weight of the composition.

The segmented copolymer composition may be present in a coating, forexample. Such a coating may be characterized by a contact angle of wateron a coating surface of greater than 90°. Such a coating may becharacterized by a coefficient of friction, measured at 90% relativehumidity, less than 0.7. Such a coating may be characterized by anaverage kinetic delay of surface ice formation of at least 5 minutes at−10° C.

Some variations provide a low-friction, low-adhesion material (e.g.,coating or bulk material) comprising:

a substantially continuous matrix containing a first component;

a plurality of inclusions containing a second component, wherein theinclusions are dispersed within the matrix;

wherein one of the first component or the second component is alow-surface-energy polymer having a surface energy between about 5 mJ/m²to about 50 mJ/m², and the other of the first component or the secondcomponent is a hygroscopic material,

and wherein the continuous matrix and the inclusions form a lubricatingsurface layer in the presence of humidity.

In some embodiments, the surface energy of the low-surface-energypolymer is between about 10 mJ/m² to about 40 mJ/m². In some preferredembodiments, the low-surface-energy polymer is a fluoropolymer selectedfrom the group consisting of polyfluoroethers, perfluoropolyethers,polyfluoroacrylates, polyfluorosiloxanes, and combinations thereof.

The hygroscopic material may be selected from the group consisting ofpoly(acrylic acid), poly(ethylene glycol), poly(2-hydroxyethylmethacrylate), poly(vinyl imidazole), poly(2-methyl-2-oxazoline),poly(2-ethyl-2-oxazoline), poly(vinylpyrolidone), cellulose, modifiedcellulose, carboxymethyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, methyl cellulose, hydrogels, PEG diacryalate,monoacrylate, and combinations thereof.

In some low-friction, low-adhesion materials, the low-surface-energypolymer and the hygroscopic material are covalently connected in a blockcopolymer. For example, the block copolymer may be a segmented copolymercomposition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0, such as from about 0.1 to about 1.5.

In some embodiments, the fluoropolymers include a segmented copolymerbased on fluoropolymer and poly(ethylene glycol), having the structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol), poly(tetrahydrofuran), poly(glycolic acid),poly(caprolactone), poly(ethylene adipate), poly(hydroxybutyrate),poly(hydroxyalkanoate), and combinations thereof.

The low-surface-energy polymer and/or the hygroscopic material may besurface-treated. The low-friction, low-adhesion material optionallyfurther contains one or more additional components selected from thegroup consisting of a particulate filler, a pigment, a dye, aplasticizer, a flame retardant, a flattening agent, and a substrateadhesion promoter.

A particulate filler may be selected from the group consisting ofsilica, alumina, silicates, talc, aluminosilicates, barium sulfate,mica, diatomite, calcium carbonate, calcium sulfate, carbon,wollastonite, and combinations thereof.

Optionally, a particulate filler is surface-modified with a compoundselected from the group consisting of fatty acids, silanes,alkylsilanes, fluoroalkylsilanes, silicones, alkyl phosphonates, alkylphosphonic acids, alkyl carboxylates, alkyldisilazanes, and combinationsthereof.

The low-friction, low-adhesion material may be characterized by a waterabsorption capacity of at least 10 wt % water based on total weight ofthe low-friction, low-adhesion material. The low-friction, low-adhesionmaterial may be characterized by a surface contact angle of water ofgreater than 90°. The low-friction, low-adhesion material may becharacterized by a coefficient of friction, measured at 90% relativehumidity, less than 0.7. The low-friction, low-adhesion material may becharacterized by an average delay in the formation of ice on a surfaceof the low-friction, low-adhesion material of at least 10 minutes at−10° C.

Variations of the invention also provide a precursor material for alow-friction, low-adhesion material, the precursor material comprising:

a hardenable material capable of forming a substantially continuousmatrix containing a first component; and

a plurality of inclusions containing a second component, wherein theinclusions are dispersed within the hardenable material,

wherein one of the first component or the second component is alow-surface-energy polymer having a surface energy between about 5 mJ/m²to about 50 mJ/m², and the other of the first component or the secondcomponent is a hygroscopic material.

In some embodiments, the surface energy of the low-surface-energypolymer is between about 10 mJ/m² to about 40 mJ/m². In someembodiments, the low-surface-energy polymer is a fluoropolymer, such asone selected from the group consisting of polyfluoroethers,perfluoropolyethers, polyfluoroacrylates, polyfluorosiloxanes, andcombinations thereof.

In some embodiments, the hygroscopic material is selected from the groupconsisting of poly(acrylic acid), poly(ethylene glycol),poly(2-hydroxyethyl methacrylate), poly(vinyl imidazole),poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline),poly(vinylpyrolidone), cellulose, modified cellulose, carboxymethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose, hydrogels, PEG diacryalate, monoacrylate, and combinationsthereof.

The low-surface-energy polymer and the hygroscopic material may becovalently connected, or are capable of being covalently connected, in ablock copolymer. For example, a block copolymer may be a segmentedcopolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0, such as from about 0.1 to about 1.5.

In some embodiments, the fluoropolymers include a fluoropolymer havingthe structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol) (also known as poly(propylene oxide)),poly(tetrahydrofuran), poly(glycolic acid), poly(caprolactone),poly(ethylene adipate), poly(hydroxybutyrate), poly(hydroxyalkanoate),and combinations thereof.

The low-surface-energy polymer and/or the hygroscopic material may besurface-treated, either prior to introduction into the precursormaterial or prior to conversion of the precursor material to thelow-friction, low-adhesion material.

The precursor material may further contain one or more additionalcomponents selected from the group consisting of a particulate filler, apigment, a dye, a plasticizer, and a flame retardant. Alternatively, oradditionally, such additional components may be introduced during theconversion of the precursor material to the low-friction, low-adhesionmaterial, or to the low-friction, low-adhesion material after it isformed.

Specific particulate fillers include, for example, silica, alumina,silicates, talc, aluminosilicates, barium sulfate, mica, diatomite,calcium carbonate, calcium sulfate, carbon, wollastonite, andcombinations thereof. The particulate fillers may be surface-modifiedwith a compound selected from the group consisting of fatty acids,silanes, silicones, alkyl phosphonates, alkyl phosphonic acids, alkylcarboxylates, and combinations thereof. Optionally, the fillers may besurface-modified with a hydrophobic material, such as (but not limitedto) an alkylsilane, a fluoroalkylsilane, and/or an alkyldisilazane(e.g., hexamethyldisilazane).

In some variations of the invention, a material or coating precursor isapplied to a substrate (such as a surface of an automobile or aircraft)and allowed to react, cure, or harden to form a final coating, whereinthe material, coating precursor, or final coating contains a segmentedcopolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the structure of some variations of the invention,providing a low-friction, low-adhesion material.

FIG. 2 illustrates the mode of action according to some variations,showing an insect sliding off the surface following impact.

FIG. 3 includes a table of experimental data from Examples A, B, C, D,E, and F described herein.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The materials, compositions, structures, systems, and methods of thepresent invention will be described in detail by reference to variousnon-limiting embodiments.

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with the accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs.

Unless otherwise indicated, all numbers expressing conditions,concentrations, dimensions, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least upona specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

Some variations of this invention are premised on the discovery of amaterial that possesses both low surface energy (for low adhesion) andthe ability to absorb water. A structured material or coating, asdisclosed, passively absorbs water from the atmosphere and then expelsthis water upon impact with the impacting debris, to create alubrication/self-cleaning layer and reduce the friction and adhesion ofthe impacting body (such as an insect) on the surface. The material maybe used as a coating or as a surface.

The coating in some embodiments may be characterized as “bugphobic,”which is intended to mean the coating has relatively low adhesion withan impacting bug. Because these materials trap a layer of water near thesurface, they also can delay the formation of ice, in some embodiments.The coating in some embodiments may be characterized as “icephobic,”which is intended to mean the coating is capable of delaying theformation of ice and/or causing a freezing-point depression of ice,compared to a bare substrate. The lubricating component has the abilityto trap and organize a layer of water at the surface to both inhibitfreezing and reduce adhesion forces in ice that does begin to accumulateon the surface.

In contrast to prior structures and methods, the disclosed material canabsorb water from the air and use this water as a lubricant to wash andremove debris from the surface. The surface contains domains of alow-surface-energy polymer (such as, but not limited to, afluoropolymer) providing low adhesion, and domains of a hygroscopicmaterial. Without being limited by theory, it is speculated that in someembodiments, the hygroscopic material absorbs water and releases some ofit back onto the surface during impact. The atmospheric water is thuscaptured as a lubricant and is a continually available, renewableresource.

By reducing friction, the debris is less likely to embed in or otherwiseattach to the surface and instead will slough off the surface (asillustrated in FIG. 2, where debris is depicted as a wasp). Debris maybe organic or inorganic and may include insects, dirt, dust, soot, ash,pollutants, particulates, ice, seeds, plant or animal fragments, plantor animal waste products, combinations or derivatives of any of theforegoing, and so on.

The domains of hygroscopic material exist throughout the material, inboth planar and depth dimensions. The anti-adhesion function is retainedeven after abrasion of the top layer of the material.

In some variations, low-friction and low-adhesion structures are createdby a heterogeneous microstructure comprising a low-surface-energypolymer that is interspersed with hygroscopic domains (lubricatinginclusions). Debris impacting the surface has low adhesion energy withthe surface, due to the presence of the low-surface-energy polymer, andthe debris will not remain on the surface.

Preferred embodiments employ fluoropolymers, without limitation of theinvention, as described in more detail below. A preferred technique tocompatiblize fluoropolymers and hygroscopic materials is the use ofsegmented polyurethane or urea systems. These species demonstrate stronghydrogen bonding potential between them and as a result can createstrong associative forces between the chains. In order to produceelastomeric materials, regions of highly flexible and weakly interactingchains (soft segments) must be incorporated with strongly associatingelements (hard segments) and this can be provided in a segmentedcopolymerization scheme. Segmented copolymers provide a straightforwardsynthetic route toward block architectures using segments with vastlydiffering properties. Such synthesis results in chains that possessalternating hard and soft segments composed of regions of high urethanebond density and the chosen soft segment component (e.g., fluoropolymeror hygroscopic element), respectively. This covalent linkage ofdissimilar hard and soft blocks drives the systems to microphaseseparation and creates regions of flexible soft blocks surroundingregions of hard blocks. The associative forces among the hard segmentsprevent flow under stress and can produce elastomeric materials capableof displaying high elongation and tensile strength.

In a specific embodiment of the disclosure, there is provided asegmented copolymer composition. The composition comprises one or moreα,ω (alpha, omega)-amine-terminated or α,ω (alpha,omega)-hydroxyl-terminated polyfluoropolymer first soft segments havingan average molecular weight of between about 500 grams per mole to about10,000 grams per mole. The exemplary composition further comprises oneor more polyethylene glycol second soft segments having an averagemolecular weight of between about 500 grams per mole to about 10,000grams per mole. A total content of the one or more first soft segmentsand the one or more second soft segments is present in an amount of fromabout 40% by weight to about 90% by weight, based on a total weightpercent of the composition. The composition further comprises one ormore hard segments present in an amount of from about 15% by weight toabout 50% by weight, based on the total weight percent of thecomposition. The one or more hard segments comprise a combination of oneor more isocyanate species and one or more low-molecular-weight polyolor polyamine chain extenders or crosslinkers. Preferred compositions arecharacterized a contact angle of water on the surface >90° and by adelay in the formation of ice on the surface.

Some variations provide a segmented copolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0.

It is noted that (α,ω)-terminated polymers are terminated at each end ofthe polymer. The α-termination may be the same or different than theco-termination. Also it is noted that in this disclosure,“(α,ω)-termination” includes branching at the ends, so that the numberof terminations may be greater than 2 per polymer molecule. The polymersherein may be linear or branched, and there may be various terminationsand functional groups within the polymer chain, besides the end (α,ω)terminations.

In some embodiments, the molar ratio of the second soft segments to thefirst soft segments is from about 0.1 to about 1.5. In variousembodiments, the molar ratio of the second soft segments to the firstsoft segments is about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 1.95.

In this description, “polyurethane” is a polymer comprising a chain oforganic units joined by carbamate (urethane) links, where “urethane”refers to N(H)—(C═O)—O—. Polyurethanes are generally produced byreacting an isocyanate containing two or more isocyanate groups permolecule with one or more polyols containing on average two or morehydroxyl groups per molecule, in the presence of a catalyst.

Polyols are polymers in their own right and have on average two or morehydroxyl groups per molecule. For example, α,ω-hydroxyl-terminatedperfluoropolyether is a type of polyol.

“Isocyanate” is the functional group with the formula —N═C═O. For thepurposes of this disclosure, S—C(═O)—N(H)—R is considered a derivativeof isocyanate.

“Polyfluoroether” refers to a class of polymers that contain an ethergroup—an oxygen atom connected to two alkyl or aryl groups, where atleast one hydrogen atom is replaced by a fluorine atom in an alkyl oraryl group.

“Perfluoropolyether” (PFPE) is a highly fluorinated subset ofpolyfluoroethers, wherein all hydrogen atoms are replaced by fluorineatoms in the alkyl or aryl groups.

“Polyurea” is a polymer comprising a chain of organic units joined byurea links, where “urea” refers to N(H)—(C═O)—N(H)—. Polyureas aregenerally produced by reacting an isocyanate containing two or moreisocyanate groups per molecule with one or more multifunctional amines(e.g., diamines) containing on average two or more amine groups permolecule, in the presence of a catalyst.

A “chain extender or crosslinker” is a compound (or mixture ofcompounds) that link long molecules together and thereby complete apolymer reaction. Chain extenders or crosslinkers are also known ascuring agents, curatives, or hardeners. In polyurethane/urea systems, acurative is typically comprised of hydroxyl-terminated oramine-terminated compounds which react with isocyanate groups present inthe mixture. Diols as curatives form urethane linkages, while diaminesas curatives form urea linkages. The choice of chain extender orcrosslinker may be determined by end groups present on a givenprepolymer. In the case of isocyanate end groups, curing can beaccomplished through chain extension using multifunctional amines oralcohols, for example. Chain extenders or crosslinkers can have anaverage functionality greater than 2 (such as 3 or greater), i.e. beyonddiols or diamines.

The one or more chain extenders or crosslinkers (or reaction productsthereof) may be present in a concentration, in the segmented copolymercomposition, from about 0.01 wt % to about 10 wt %, such as about 0.05wt % to about 1 wt %.

As meant herein, a “low-surface-energy polymer” means a polymer, or apolymer-containing material, with a surface energy of no greater than 50mJ/m². The principles of the invention may be applied tolow-surface-energy materials with a surface energy of no greater than 50mJ/m², in general (i.e., not necessarily limited to polymers).

In some embodiments, the low-surface-energy polymer includes afluoropolymer, such as (but not limited to) a fluoropolymer selectedfrom the group consisting of polyfluoroethers, perfluoropolyethers,fluoroacrylates, fluorosilicones, and combinations thereof.

In these or other embodiments, the low-surface-energy polymer includes asiloxane. A siloxane contains at least one Si—O—Si linkage. Thelow-surface-energy polymer may consist of polymerized siloxanes orpolysiloxanes (also known as silicones). One example ispolydimethylsiloxane.

In some embodiments, the fluoropolymers are selected from the groupconsisting of perfluoropolyethers, polyfluoroacrylates,polyfluorosiloxanes, and combinations thereof. In certain embodiments,the fluoropolymers include a fluoropolymer segmented copolymer withpoly(ethylene glycol) having the structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol), poly(tetrahydrofuran), poly(glycolic acid),poly(caprolactone), poly(ethylene adipate), poly(hydroxybutyrate),poly(hydroxyalkanoate), and combinations thereof.

In some embodiments, the isocyanate species is selected from the groupconsisting of 4,4′-methylenebis(cyclohexyl isocyanate), hexamethylenediisocyanate, cycloalkyl-based diisocyanates, tolylene-2,4-diisocyanate,4,4′-methylenebis(phenyl isocyanate), isophorone diisocyanate, andcombinations or derivatives thereof.

The polyol or polyamine chain extender possesses a functionality of 2 orgreater, in some embodiments. At least one polyol or polyamine chainextender may be selected from the group consisting of 1,4-butanediol,1,3-propanediol, 1,2-ethanediol, glycerol, trimethylolpropane,ethylenediamine, isophoronediamine, diaminocyclohexane, and homologues,derivatives, or combinations thereof.

Following a suitable chemical reaction, the segmented copolymercomposition contains, in a hard segment, the reacted form of the one ormore isocyanate species, combined with the reacted form of the one ormore polyol or polyamine chain extenders or crosslinkers. In someembodiments, the hard segment is present in an amount from about 5 wt %to about 60 wt %, based on total weight of the composition.

The segmented copolymer composition may be present in a coating, forexample. Such a coating may be characterized by a contact angle of wateron a coating surface of greater than 90°. Such a coating may becharacterized by an average kinetic delay of surface ice formation of atleast 5 minutes at −10° C.

The structure of some variations of the invention is shown in FIG. 1.FIG. 1 depicts the structure of a coating or surface with low-frictionand self-cleaning properties.

The structure 100 of FIG. 1 includes a continuous matrix 110. A“continuous matrix” (or equivalently, “substantially continuous matrix”)means that the matrix material is present in a form that includeschemical bonds among molecules of the matrix material. An example ofsuch chemical bonds is crosslinking bonds between polymer chains. In asubstantially continuous matrix 110, there may be present variousdefects, cracks, broken bonds, impurities, additives, and so on. Thestructure 100 further includes a plurality of inclusions 120, dispersedwithin the matrix 110, each of the inclusions 120 comprising ahygroscopic material.

Optionally, the continuous matrix 110 may further comprise one or moreadditives selected from the group consisting of fillers, colorants, UVabsorbers, defoamers, plasticizers, viscosity modifiers, densitymodifiers, catalysts, and scavengers.

The mode of action according to some variations is shown in FIG. 2. Thestructure of FIG. 2 includes a continuous matrix 210 and a plurality ofinclusions 220. FIG. 2 illustrates the response of the surface 200 to animpact of debris, which in this illustration is a bug 240 (e.g, wasp),as a non-limiting example. The bug 240 slides across the surface(200/205) instead of breaking apart, ultimately leaving the surface 205and thereby not leaving behind debris bound to the material.

Some variations provide a low-friction, low-adhesion material (e.g.,coating or bulk material) comprising:

a substantially continuous matrix containing a first component;

a plurality of inclusions containing a second component, wherein theinclusions are dispersed within the matrix;

wherein one of the first component or the second component is alow-surface-energy polymer having a surface energy between about 5 mJ/m²to about 50 mJ/m², and the other of the first component or the secondcomponent is a hygroscopic material,

and wherein the continuous matrix and the inclusions form a lubricatingsurface layer in the presence of humidity.

In some embodiments, the surface energy of the low-surface-energypolymer is between about 10 mJ/m² to about 40 mJ/m², such as about 10,15, 20, 25, 30, 35, or 40, mJ/m². In some preferred embodiments, thelow-surface-energy polymer is a fluoropolymer selected from the groupconsisting of polyfluoroethers, perfluoropolyethers,polyfluoroacrylates, polyfluorosiloxanes, and combinations thereof.

The hygroscopic material may be selected from the group consisting ofpoly(acrylic acid), poly(ethylene glycol), poly(2-hydroxyethylmethacrylate), poly(vinyl imidazole), poly(2-methyl-2-oxazoline),poly(2-ethyl-2-oxazoline), poly(vinylpyrolidone), cellulose, modifiedcellulose, carboxymethyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, methyl cellulose, hydrogels, PEG diacryalate,monoacrylate, and combinations thereof.

In certain embodiments, the hygroscopic material is also classified as ahydrophilic material. A hygroscopic substance will actively attract andabsorb water. A hydrophilic substance is one where water willpreferentially wet the surface, demonstrated by contact angles <90°.

The low-surface-energy polymer and the hygroscopic material may bephase-separated, i.e. they do not form a single continuous phase. Theremay be, but is not necessarily, some degree of chemical and/or physicalbonding between the low-surface-energy polymer and the hygroscopicmaterial.

The inclusions are three-dimensional objects or domains, which may be ofany shape, geometry, or aspect ratio. In a three-dimensional object, anaspect ratio of exactly 1.0 means that all three characteristic lengthscales are identical, such as in a perfect cube. The aspect ratio of aperfect sphere is also 1.0. The inclusions may be geometricallysymmetric or asymmetric. Randomly shaped asymmetric templates are,generally speaking, geometrically asymmetric. In some embodiments,inclusions are geometrically symmetric. Examples include cylinders,cones, rectangular prisms, pyramids, or three-dimensional stars.

In some embodiments, the inclusions are anisotropic. As meant herein,“anisotropic” inclusions have at least one chemical or physical propertythat is directionally dependent. When measured along different axes, ananisotropic inclusion will have some variation in a measurable property.The property may be physical (e.g., geometrical) or chemical in nature,or both.

The inclusions may be characterized as templates, domains, or regions(such as phase-separated regions). The inclusions are not a single,continuous framework in the coating. Rather, the inclusions arediscrete, non-continuous and dispersed in the continuous matrix. Thehygroscopic inclusions may be dispersed uniformly within the continuousmatrix. In some low-friction, low-adhesion materials, thelow-surface-energy polymer and the hygroscopic material are covalentlyconnected in a block copolymer, in which the inclusions and thecontinuous matrix are distinct phases of the block copolymer.

As intended herein, a “block copolymer” means a copolymer containing alinear arrangement of blocks, where each block is defined as a portionof a polymer molecule in which the monomeric units have at least oneconstitutional or configurational feature absent from the adjacentportions. Several types of block copolymers are generally possible,including AB block copolymers, ABA block copolymers, ABC blockcopolymers, segmented block copolymers, and random copolymers. Segmentedblock copolymers are preferred, in some embodiments of the invention.

For example, a block copolymer may be a segmented copolymer compositioncomprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0, such as from about 0.1 to about 1.5.

In some embodiments, the fluoropolymers include a fluoropolymer havingthe structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol), poly(tetrahydrofuran), poly(glycolic acid),poly(caprolactone), poly(ethylene adipate), poly(hydroxybutyrate),poly(hydroxyalkanoate), and combinations thereof.

A wide range of concentrations of components may be present in thelow-friction, low-adhesion material. For example, the continuous matrixmay be from about 5 wt % to about 95 wt %, such as from about 10 wt % toabout 50 wt % of the material. The inclusions may be from about 1 wt %to about 90 wt %, such as from about 10 wt % to about 50 wt % of thecoating.

Within the component containing the low-surface-energy polymer, thelow-surface-energy polymer may be from about 50 wt % to 100 wt %, suchas about 60, 70, 80, 90, 95, or 100 wt %. Within the componentcontaining the hygroscopic material, the hygroscopic material may befrom about 50 wt % to 100 wt %, such as about 60, 70, 80, 90, 95, or 100wt %.

The low-surface-energy polymer and/or the hygroscopic material may besurface-treated, such as to adjust hydrophobicity. The low-friction,low-adhesion material optionally further contains one or more additionalcomponents selected from the group consisting of a particulate filler, apigment, a dye, a plasticizer, a flame retardant, a flattening agent,and a substrate adhesion promoter.

A particulate filler may be selected from the group consisting ofsilica, alumina, silicates, talc, aluminosilicates, barium sulfate,mica, diatomite, calcium carbonate, calcium sulfate, carbon,wollastonite, and combinations thereof. The particulate fillersgenerally should be in the size range of about 5 nm to about 2 μm, suchas about 20 nm to 100 nm.

The particulate fillers may be surface-modified with a compound selectedfrom the group consisting of fatty acids, silanes, silicones, alkylphosphonates, alkyl phosphonic acids, alkyl carboxylates, andcombinations thereof. Optionally, the fillers may be surface-modifiedwith a hydrophobic material, such as (but not limited to) analkylsilane, a fluoroalkylsilane, and/or an alkyldisilazane (e.g.,hexamethyldisilazane).

In some embodiments, the low-friction, low-adhesion material furtherincludes voids. As intended herein, a “void” is a discrete region ofempty space, or space filled with air or another gas, that is enclosedwithin the continuous matrix. The voids may be open (e.g.,interconnected voids) or closed (isolated within the continuous matrix),or a combination thereof. The voids may partially surround inclusions.

The low-friction, low-adhesion material may be characterized by a waterabsorption capacity of at least 10 wt % water based on total weight ofthe low-friction, low-adhesion material. The material is characterized,according to some embodiments, by a water absorption capacity of atleast 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt % water, preferably at least 10,11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 wt % water, based on totalweight of the material.

The low-friction, low-adhesion material may be characterized by asurface contact angle of water of greater than 90° (hydrophobic). Thematerial may also be hydrophilic, i.e. characterized by an effectivecontact angle of water that is less than 90°. In various embodiments,the material is characterized by an effective contact angle of water ofabout 70°, 75°, 80°, 85°, 90°, 95°, 100°, or higher.

The material may also be lipophobic or partially lipophobic in someembodiments. In various embodiments, the material is characterized by aneffective contact angle of hexadecane (as a measure of lipophobicity) ofabout 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, or higher.

The material may simultaneously have hydrophobic and lipophobicproperties. In certain embodiments, the material is characterized by aneffective contact angle of water of at least 90° (such as about 95-100°)and simultaneously an effective contact angle of hexadecane of at least60° (such as about 65°). In certain embodiments, the material ischaracterized by an effective contact angle of water of at least 80°(such as about 80-85°) and simultaneously an effective contact angle ofhexadecane of at least 70° (such as about 75-80°).

In some embodiments, the material is characterized by a coefficient offriction, measured at 40-55% (e.g. 50%) relative humidity and roomtemperature, less than 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3. In theseor other embodiments, the material is characterized by a coefficient offriction, measured at 85% relative humidity and room temperature, lessthan 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.2. The low-friction,low-adhesion material may be characterized by a coefficient of friction,measured at 90% relative humidity, less than 0.7.

The coefficient of friction is relatively low due to the presence of alubricating surface layer. By a “lubricating surface layer in thepresence of humidity,” it is meant a layer, multiple layers, a partiallayer, or an amount of substance that lubricates the substrate such thatit has a lower coefficient of friction compared to the substrate withoutthe material present, when in the presence of some amount of atmospherichumidity.

The specific level of humidity is not regarded as critical, but ingeneral may range from about 1% to 100%, typically about 30% to about70% relative humidity. Relative humidity is the ratio of the water vapordensity (mass per unit volume) to the saturation water vapor density.Relative humidity is also approximately the ratio of the actual to thesaturation vapor pressure.

The substance that lubricates the substrate is primarily water, but itshould be noted that other components from the environment may bepresent in the lubricating surface layer, including oils, metals, dust,dissolved gases, dissolved aqueous components, suspended non-aqueouscomponents, fragments of debris, fragments of polymers, and so on.

The material may be characterized by a delay in the formation of ice ona surface of the material. For example, when a material surface is heldat −10° C., the material provided by the invention may be characterizedby an average delay in the formation of ice on the surface of at leastabout 10, 15, 20, 25, 30 minutes, or more.

In various embodiments, the material is a coating and/or is present at asurface of an object or region. The material may be utilized inrelatively small applications, such as lens coatings, or for largestructures, such as aircraft wings. In principle, the material could bepresent within a bulk region of an object or part, or could contain atemporary, protective laminating film for storage or transport, which islater removed to adhere to the vehicle, for example.

Variations of the invention also provide a precursor material for alow-friction, low-adhesion material, the precursor material comprising:

a hardenable material capable of forming a substantially continuousmatrix containing a first component; and

a plurality of inclusions containing a second component, wherein theinclusions are dispersed within the hardenable material,

wherein one of the first component or the second component is alow-surface-energy polymer having a surface energy between about 5 mJ/m²to about 50 mJ/m², and the other of the first component or the secondcomponent is a hygroscopic material.

In some embodiments, the surface energy of the low-surface-energypolymer is between about 10 mJ/m² to about 40 mJ/m², such as about 10,15, 20, 25, 30, 35, or 40, mJ/m². In some embodiments, thelow-surface-energy polymer is a fluoropolymer, such as one selected fromthe group consisting of polyfluoroethers, perfluoropolyethers,polyfluoroacrylates, polyfluorosiloxanes, and combinations thereof.

In some embodiments, the hygroscopic material is selected from the groupconsisting of poly(acrylic acid), poly(ethylene glycol),poly(2-hydroxyethyl methacrylate), poly(vinyl imidazole),poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline),poly(vinylpyrolidone), cellulose, modified cellulose, carboxymethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose, hydrogels, PEG diacryalate, monoacrylate, and combinationsthereof.

The low-surface-energy polymer and the hygroscopic material may becovalently connected, or are capable of being covalently connected, in ablock copolymer. For example, a block copolymer may be a segmentedcopolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0, such as from about 0.1 to about 1.5.

In some embodiments, the fluoropolymers include a fluoropolymer havingthe structure:

wherein:X═CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50;m=1 to 100; andn=1 to 100.

In some embodiments, the polyesters or polyethers are selected from thegroup consisting of poly(oxymethylene), poly(ethylene glycol),poly(propylene glycol), poly(tetrahydrofuran), poly(glycolic acid),poly(caprolactone), poly(ethylene adipate), poly(hydroxybutyrate),poly(hydroxyalkanoate), and combinations thereof.

The low-surface-energy polymer and/or the hygroscopic material may besurface-treated, either prior to introduction into the precursormaterial or prior to conversion of the precursor material to thelow-friction, low-adhesion material.

The precursor material may further contain one or more additionalcomponents selected from the group consisting of a particulate filler, apigment, a dye, a plasticizer, a flame retardant, a flattening agent,and a substrate adhesion promoter. Alternatively, or additionally, suchadditional components may be introduced during the conversion of theprecursor material to the low-friction, low-adhesion material, or to thelow-friction, low-adhesion material after it is formed.

Specific particulate fillers include, for example, silica, alumina,silicates, talc, aluminosilicates, barium sulfate, mica, diatomite,calcium carbonate, calcium sulfate, carbon, wollastonite, andcombinations thereof. The particulate fillers generally should be in thesize range of about 5 nm to about 2 μm, such as about 20 nm to 100 nm.

The particulate fillers may be surface-modified with a compound selectedfrom the group consisting of fatty acids, silanes, silicones, alkylphosphonates, alkyl phosphonic acids, alkyl carboxylates, andcombinations thereof. Optionally, the fillers may be surface-modifiedwith a hydrophobic material, such as (but not limited to) analkylsilane, a fluoroalkylsilane, and/or an alkyldisilazane (e.g.,hexamethyldisilazane).

Any known methods to fabricate these materials or coatings may beemployed. Notably, these materials or coatings may utilize synthesismethods that enable simultaneous deposition of components or precursormaterials to reduce fabrication cost and time. In particular, thesematerials or coatings may be formed by a one-step process, in someembodiments. In other embodiments, these materials or coatings may beformed by a multiple-step process.

The low-friction, low-adhesion hydrophobic or hydrophilic material, insome embodiments, is formed from a precursor material (or combination ofmaterials) that may be provided, obtained, or fabricated from startingcomponents. The precursor material is capable of hardening or curing insome fashion, to form a substantially continuous matrix along with aplurality of inclusions, dispersed within the matrix. The precursormaterial may be a liquid; a multiphase liquid; a multiphase slurry,emulsion, or suspension; a gel; or a dissolved solid (in solvent), forexample.

The low-surface-energy polymer and the hygroscopic material may be inthe same phase or in different phases. In some embodiments, thelow-surface-energy polymer is in liquid or dissolved form while thehygroscopic material is in dissolved-solid or suspended solid form. Insome embodiments, the low-surface-energy polymer is dissolved-solid orsuspended-solid form while the hygroscopic material is in liquid ordissolved form. In some embodiments, the low-surface-energy polymer andthe hygroscopic material are both in liquid form. In some embodiments,the low-surface-energy polymer and the hygroscopic material are both indissolved (solvent) form.

In some variations of the invention, a material or coating precursor isapplied to a substrate (such as a surface of an automobile or aircraft)and allowed to react, cure, or harden to form a final coating, whereinthe material, coating precursor, or final coating contains a segmentedcopolymer composition comprising:

(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein the fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated;

(b) one or more second soft segments selected from polyesters orpolyethers, wherein the polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated;

(c) one or more isocyanate species, or a reacted form thereof,possessing an isocyanate functionality of 2 or greater; and

(d) one or more polyol or polyamine chain extenders or crosslinkers, ora reacted form thereof,

wherein the molar ratio of the second soft segments to the first softsegments is less than 2.0.

In some embodiments, the hygroscopic material is also hardenable, eitheralone or in combination with the low-surface-energy polymer. Forinstance, a low-surface-energy polymer and a hygroscopic polymer mayform a high-molecular-weight block copolymerize and thus harden. Incertain embodiments, the hygroscopic material assists in the curability(hardenability) of the low-surface-energy polymer.

In some embodiments, a precursor material is prepared and then dispensed(deposited) over an area of interest. Any known methods to depositprecursor materials may be employed. A fluid precursor material allowsfor convenient dispensing using spray coating or casting techniques overa large area, such as the scale of a vehicle or aircraft.

The fluid precursor material may be applied to a surface using anycoating technique, such as (but not limited to) spray coating, dipcoating, doctor-blade coating, spin coating, air knife coating, curtaincoating, single and multilayer slide coating, gap coating,knife-over-roll coating, metering rod (Meyer bar) coating, reverse rollcoating, rotary screen coating, extrusion coating, casting, or printing.Because relatively simple coating processes may be employed, rather thanlithography or vacuum-based techniques, the fluid precursor material maybe rapidly sprayed or cast in thin layers over large areas (such asmultiple square meters).

When a solvent or carrier fluid is present in the fluid precursormaterial, the solvent or carrier fluid may include one or more compoundsselected from the group consisting of water, alcohols (such as methanol,ethanol, isopropanol, or tert-butanol), ketones (such as acetone, methylethyl ketone, or methyl isobutyl ketone), hydrocarbons (e.g., toluene),acetates (such as tert-butyl acetate), acids (such as organic acids),bases, and any mixtures thereof. When a solvent or carrier fluid ispresent, it may be in a concentration of from about 10 wt % to about 99wt % or higher, for example.

The precursor material may be converted to an intermediate material orthe final material using any one or more of curing or other chemicalreactions, or separations such as removal of solvent or carrier fluid,monomer, water, or vapor. Curing refers to toughening or hardening of apolymeric material by cross-linking of polymer chains, assisted byelectromagnetic waves, electron beams, heat, and/or chemical additives.Chemical removal may be accomplished by heating/flashing, vacuumextraction, solvent extraction, centrifugation, etc. Physicaltransformations may also be involved to transfer precursor material intoa mold, for example. Additives may be introduced during the hardeningprocess, if desired, to adjust pH, stability, density, viscosity, color,or other properties, for functional, ornamental, safety, or otherreasons.

The overall thickness of the final material or coating may be from about1 μm to about 1 cm or more, such as about 10 μm, 20 μm, 25 μm, 30 μm, 40μm, 50 μm, 75 μm, 100 μm, 500 μm, 1 mm, 1 cm, or 10 cm. Relatively thickcoatings offer good durability and mechanical properties, such as impactresistance, while preferably being relatively lightweight.

EXAMPLES

Materials.

Poly(ethylene glycol) (PEG) with molecular weight (M_(n)) of 3,400g/mol, 4,4′-methylenebis(cyclohexyl isocyanate) (HMDI), 1,4-butanediol(BD), and dibutyltin dilaurate (DBTDL) were purchased from Aldrich.Fluorolink D4000 and Fluorolink E10-H perfluoropolyether were purchasedfrom Solvay Specialty Polymers. All chemicals were used as receivedwithout further purification.

Example A: Fluoropolymer Control

Flurolink D4000 perfluoropolyether (4 g) is charged to a vial followedby HMDI (0.786 g). A small PTFE-coated stir bar is introduced and thevial is placed in a 100° C. oil bath to stir. The reaction is vortexedaggressively after achieving a temperature of 100° C., and then left tostir for 1 hour. After this step, the resin is poured into a 3″×3″ PTFEmold to flash off solvent and cure the film at room temperatureovernight.

Example B: Perfluoropolyether/Poly(Ethylene Glycol) Block Copolymer

PEG (1.5 mmoles, 5.1 g) and HMDI (15 mmoles, 3.94 g) are added into a3-neck flask equipped with a mechanical stirrer. The reaction flask isplaced in a 100° C. oil bath. The reaction is carried out under argon.Once PEG is melted and dissolved in the HMDI, 10 μl of DBTDL is added tothe mix. The reaction mixture is stirred at 100° C. for 1 hour.Fluorolink D4000 (1.5 mmoles, 6 g) is added and stirring is continuedfor another 1.75 hours. The reaction flask is removed from the 100° C.oil bath, and allowed to cool down before adding THF (10 ml) and BD (12mmoles, 1.08 g) dissolved in THF (2 mL). The THF and BD are added to theviscous resin and vortexed to disperse and thin the overall mixture(precursor material).

The precursor material resin is then poured into a 3″×3″ PTFE mold toflash off solvent and cure the precursor material film at roomtemperature overnight. The next day the film is placed in an 80° C. ovenfor 4 hours to complete the cure. The cured material is aperfluoropolyether/poly(ethylene glycol) block copolymer with a molarratio of PEG to perfluoroether of 1.0.

Example B2: Perfluoropolyether/Poly(Ethylene Glycol) Block Copolymer

PEG (1.5 mmoles, 5.1 g) and HMDI (15 mmoles, 3.94 g) are added into a3-neck flask equipped with a mechanical stirrer. The reaction flask isplaced in a 100° C. oil bath. Once PEG melts and dissolves in the HMDI,10 μl of DBTDL is added to the mix. The reaction mixture is stirred at100° C. for 1 hour. Fluorolink D4000 (1.5 mmoles, 6 g) is added andstirring is continued for another 1.75 hours. The reaction flask isremoved from the 100° C. oil bath, and allowed to cool down beforeadding THF (10 ml), BYK-LP X 22325 and vortexed to disperse silica inthe mixture. 1,4-Butanediol (12 mmoles, 0.161 g) dissolved in THF (2 mL)is added to the mixture and vortexed.

The precursor material resin is then poured into a 3″×3″ PTFE mold toflash off solvent and cure the precursor material film at roomtemperature overnight. The next day the film is placed in an 80° C. ovenfor 4 hours to complete the cure. The cured material is aperfluoropolyether/poly(ethylene glycol) block copolymer with a molarratio of PEG to perfluoroether of 1.0, further comprising a silicafiller.

Example C: Perfluoropolyether/Poly(Ethylene Glycol) Block Copolymer

The procedure described in Example B is followed, except that the curedmaterial is a perfluoropolyether/poly(ethylene glycol) block copolymerwith a molar ratio of PEG to perfluoroether of 1.33.

Example D: Perfluoropolyether/Poly(Ethylene Glycol) Block Copolymer

PEG (2 mmoles, 6.8 g) and HMDI (12.8 mmoles, 3.36 g) are added into a3-neck flask equipped with a mechanical stirrer. The reaction flask isplaced in a 100° C. oil bath. The reaction is carried out under argon.Once PEG is melted and dissolved in the HMDI, 10 μl of DBTDL is added tothe mix. The reaction mixture is stirred at 100° C. for 1 hour.Fluorolink E10-H (2 mmoles, 3 g) is added and stirring continues another1.75 hours. The reaction flask is removed from 100° C. oil bath, andallowed to cool down before adding THF (8 mL) and BD (8.8 mmoles, 0.8 g)dissolved in THF (2 mL).

The precursor material resin is then poured into a 3″×3″ PTFE mold toflash off solvent and cure the precursor material film at roomtemperature overnight. The next day the film is placed in an 80° C. ovenfor 4 hours to complete the cure. The cured material is aperfluoropolyether/poly(ethylene glycol) block copolymer with a molarratio of PEG to perfluoroether of 1.0.

Comparative Example E: Perfluoropolyether/Poly(Ethylene Glycol) BlockCopolymer with High PEG Fraction

PEG (3 mmoles, 10.2 g) and HMDI (20 mmoles, 5.25 g) are added into a3-neck flask equipped with a mechanical stirrer. The reaction flask isplaced in a 100° C. oil bath. The reaction is carried out under argon.Once PEG is melted and dissolved in the HMDI, 12 μl of DBTDL is added tothe mix. The reaction mixture is stirred at 100° C. for 1 hour.Fluorolink D4000 (1 mmoles, 4 g) is added and stirring continues foranother 2 hours. The reaction flask is removed from 100° C. oil bath,and allowed to cool down before adding THF (10 mL) and BD (16 mmoles,1.44 g) dissolved in THF (3 mL).

The precursor material resin is then poured into a 3″×3″ PTFE mold toflash off solvent and cure the precursor material film at roomtemperature overnight. The next day the film is placed in an 80° C. ovenfor 4 hours to complete the cure. The cured material is aperfluoropolyether/poly(ethylene glycol) block copolymer with a molarratio of PEG to perfluoroether of 3.0.

Comparative Example F: Perfluoropolyether/Poly(Ethylene Glycol) BlockCopolymer with High PEG Fraction

PEG (3 mmoles, 10.2 g) and HMDI (12.8 mmoles, 3.36 g) are added into a3-neck flask equipped with a mechanical stirrer. The reaction flask isplaced in a 100° C. oil bath. The reaction is carried out under argon.Once PEG is melted and dissolved in the HMDI, 12 μl of DBTDL is added tothe mix. The reaction mixture is stirred at 100° C. for 1 hour.Fluorolink E10-H (1 mmoles, 1.5 g) is added and stirring continues foranother 2 hours. The reaction flask is removed from 100° C. oil bath,and allowed to cool down before adding THF (8 mL) and BD (8.8 mmoles,0.8 g) dissolved in THF (2 mL).

The precursor material resin is then poured into a 3″×3″ PTFE mold toflash off solvent and cure the precursor material film at roomtemperature overnight. The next day the film is placed in an 80° C. ovenfor 4 hours to complete the cure. The cured material is aperfluoropolyether/poly(ethylene glycol) block copolymer with a molarratio of PEG to perfluoroether of 3.0.

Friction Testing.

The change in friction in response to humidity is tested byequilibrating the samples of Examples A, B, C, D, E, and F at ambient(40-55%) relative humidity or 90% relative humidity in ahumidity-controlled chamber. Then the samples are placed on avariable-angle stage and the angle is increased until a 5-gramcylindrical mass slides along the sample surface. The sliding angle isused to determine the friction constant (coefficient of friction). Thefriction change is shown for the samples of Examples A-F in the table ofFIG. 3. While the friction coefficient increases with increasedhumidity, the final result is still a smooth low-friction coating.

Ice Formation Testing.

The kinetic delay of freezing is measured by placing three 50 μL dropsof deionized water on a surface held at −10° C. with a thermoelectriccooler. The time for ice to initially form in the droplets is measured.The kinetic delay of freezing is shown for the samples of Examples A, B,C, D, E, and F and Al control in the table of FIG. 3. A bare aluminum(Al) surface has an ice formation delay of 0.2±0.1 minutes. The ExampleA fluoropolymer control demonstrates an ice formation delay of 1.3min±0.9 min.

The surprisingly long ice formation delay of materials of Examples C, D,and E may be due to the material trapping water at the surface. Withoutbeing limited by theory, it is believed that this trapped layer of watercannot freeze because the hygroscopic domains inhibit thecrystallization reaction mechanisms in the surface water. Any droplet ofwater on the surface sees liquid water instead of a coating on thesurface; ice nucleation is confined to the homogeneous nucleation regimethat is kinetically much slower than heterogeneous nucleation.

Samples from Examples B, C, and D show extended freezing delays. TheComparative Examples E and F, with 3:1 molar ratio of PEG tofluoropolymer, are characterized by freezing delays that are notablyshorter than the samples of Examples B, C, and D. Also, due to higherPEG content in Comparative Examples E and F, elevated humidity createsan undesirably tacky surface that does not allow for easy sliding on thecoating surface.

Vehicle-based cameras for surrounding awareness will require lenscoatings that will inhibit soiling in order to function. Once soiled,the camera will lose effectiveness and eventually cease functioning. Thecoatings/surfaces described herein may be used as camera lens coatings,and may be transparent.

Aircraft lose efficiency from disruption of laminar flow when insect andparticulate debris collect on the aircraft wings. This inventionprovides materials that reduce the adhesion of insect and particulatedebris on aircraft surfaces, while simultaneously inhibiting theformation of ice.

Other practical applications for the present invention include, but arenot limited to, vehicle windows, optical lenses, filters, instruments,sensors, eyeglasses, cameras, satellites, and weapon systems. Forexample, automotive applications can utilize these coatings to preventthe formation of ice or debris on back-up camera lenses or back-upsensors. The principles taught herein may also be applied toself-cleaning materials, anti-adhesive coatings, corrosion-freecoatings, etc.

In this detailed description, reference has been made to multipleembodiments and to the accompanying drawings in which are shown by wayof illustration specific exemplary embodiments of the invention. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatmodifications to the various disclosed embodiments may be made by askilled artisan.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

The embodiments, variations, and figures described above should providean indication of the utility and versatility of the present invention.Other embodiments that do not provide all of the features and advantagesset forth herein may also be utilized, without departing from the spiritand scope of the present invention. Such modifications and variationsare considered to be within the scope of the invention defined by theclaims.

What is claimed is:
 1. A low-friction, low-adhesion material comprising:a substantially continuous matrix containing a first component; aplurality of inclusions containing a second component, wherein saidinclusions are dispersed within said matrix; wherein one of said firstcomponent or said second component is a low-surface-energy polymerhaving a surface energy between about 5 mJ/m² to about 50 mJ/m², and theother of said first component or said second component is a hygroscopicmaterial, wherein said low-surface-energy polymer and said hygroscopicmaterial are covalently connected in a block copolymer, wherein saidfirst component is microphase-separated from said second component,wherein said continuous matrix and said inclusions are selected to forma lubricating surface layer of water in the presence of humidity, andwherein said block copolymer is a segmented copolymer compositioncomprising: (a) one or more first soft segments selected fromfluoropolymers having an average molecular weight from about 500 g/molto about 10,000 g/mol, wherein said fluoropolymers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated; (b) one or moresecond soft segments selected from polyesters or polyethers, whereinsaid polyesters or polyethers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated; (c) one or more isocyanate species, or a reactedform thereof, possessing an isocyanate functionality of 2 or greater;and (d) one or more polyol or polyamine chain extenders or crosslinkers,or a reacted form thereof, wherein the molar ratio of said second softsegments to said first soft segments is less than 2.0.
 2. Thelow-friction, low-adhesion material of claim 1, wherein said surfaceenergy of said low-surface-energy polymer is between about 10 mJ/m² toabout 40 mJ/m².
 3. The low-friction, low-adhesion material of claim 1,wherein said fluoropolymer is selected from the group consisting ofpolyfluoroethers, perfluoropolyethers, and combinations thereof.
 4. Thelow-friction, low-adhesion material of claim 1, wherein said molar ratioof said second soft segments to said first soft segments is from about0.1 to about 1.5.
 5. The low-friction, low-adhesion material of claim 1,wherein said fluoropolymers include a fluoropolymer having thestructure:

wherein: X=CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50; m=1 to 100; and n=1to
 100. 6. The low-friction, low-adhesion material of claim 1, whereinsaid polyesters or polyethers are selected from the group consisting ofpoly(oxymethylene), poly(ethylene glycol), poly(propylene glycol),poly(tetrahydrofuran), poly(glycolic acid), poly(caprolactone),poly(ethylene adipate), poly(hydroxybutyrate), poly(hydroxyalkanoate),and combinations thereof.
 7. The low-friction, low-adhesion material ofclaim 1, wherein said low-surface-energy polymer and/or said hygroscopicmaterial is surface-treated.
 8. The low-friction, low-adhesion materialof claim 1, said low-friction, low-adhesion material further comprisingone or more additional components selected from the group consisting ofa particulate filler, a pigment, a dye, a plasticizer, a flameretardant, a flattening agent, and a substrate adhesion promoter.
 9. Thelow-friction, low-adhesion material of claim 1, wherein said particulatefiller is selected from the group consisting of silica, alumina,silicates, talc, aluminosilicates, barium sulfate, mica, diatomite,calcium carbonate, calcium sulfate, carbon, wollastonite, andcombinations thereof.
 10. The low-friction, low-adhesion material ofclaim 9, wherein said particulate filler is surface-modified with acompound selected from the group consisting of fatty acids, silanes,alkylsilanes, fluoroalkylsilanes, silicones, alkyl phosphonates, alkylphosphonic acids, alkyl carboxylates, alkyldisilazanes, and combinationsthereof.
 11. The low-friction, low-adhesion material of claim 1, whereinsaid low-friction, low-adhesion material is characterized by a waterabsorption capacity of at least 10 wt % water based on total weight ofsaid low-friction, low-adhesion material.
 12. The low-friction,low-adhesion material of claim 1, wherein said low-friction,low-adhesion material is characterized by a surface contact angle ofwater of greater than 90°.
 13. The low-friction, low-adhesion materialof claim 1, wherein said low-friction, low-adhesion material ischaracterized by a coefficient of friction, measured at 90% relativehumidity, less than 0.7.
 14. The low-friction, low-adhesion material ofclaim 1, wherein said low-friction, low-adhesion material ischaracterized by an average delay in the formation of ice on a surfaceof said low-friction, low-adhesion material of at least 10 minutes at−10° C.
 15. A precursor material for a low-friction, low-adhesionmaterial, said precursor material comprising: a hardenable materialcapable of forming a substantially continuous matrix containing a firstcomponent; and a plurality of inclusions containing a second component,wherein said inclusions are dispersed within said hardenable material,wherein said hardenable material and said inclusions are selected toform a lubricating surface layer of water in the presence of humidity,wherein one of said first component or said second component is alow-surface-energy polymer having a surface energy between about 5 mJ/m²to about 50 mJ/m², and the other of said first component or said secondcomponent is a hygroscopic material, wherein said low-surface-energypolymer and said hygroscopic material are covalently connected, or arecapable of being covalently connected, in a block copolymer, and whereinsaid block copolymer is a segmented copolymer composition comprising:(a) one or more first soft segments selected from fluoropolymers havingan average molecular weight from about 500 g/mol to about 10,000 g/mol,wherein said fluoropolymers are (α,ω)-hydroxyl-terminated and/or(α,ω)-amine-terminated; (b) one or more second soft segments selectedfrom polyesters or polyethers, wherein said polyesters or polyethers are(α,ω)-hydroxyl-terminated and/or (α,ω)-amine-terminated; (c) one or moreisocyanate species, or a reacted form thereof, possessing an isocyanatefunctionality of 2 or greater; and (d) one or more polyol or polyaminechain extenders or crosslinkers, or a reacted form thereof, wherein themolar ratio of said second soft segments to said first soft segments isless than 2.0.
 16. The precursor material of claim 15, wherein saidsurface energy of said low-surface-energy polymer is between about 10mJ/m² to about 40 mJ/m².
 17. The precursor material of claim 15, whereinsaid fluoropolymers are selected from the group consisting ofpolyfluoroethers, perfluoropolyethers, and combinations thereof.
 18. Theprecursor material of claim 15, wherein said molar ratio of said secondsoft segments to said first soft segments is from about 0.1 to about1.5.
 19. The precursor material of claim 15, wherein said fluoropolymersinclude a fluoropolymer having the structure:

wherein: X=CH₂—(CH₂—CH₂—O)_(p)—OH wherein p=0 to 50; m=1 to 100; and n=1to
 100. 20. The precursor material of claim 15, wherein said polyestersor polyethers are selected from the group consisting ofpoly(oxymethylene), poly(ethylene glycol), poly(propylene glycol),poly(tetrahydrofuran), poly(glycolic acid), poly(caprolactone),poly(ethylene adipate), poly(hydroxybutyrate), poly(hydroxyalkanoate),and combinations thereof.
 21. The precursor material of claim 15,wherein said low-surface-energy polymer and/or said hygroscopic materialis surface-treated.
 22. The precursor material of claim 15, saidprecursor material further comprising one or more additional componentsselected from the group consisting of a particulate filler, a pigment, adye, a plasticizer, and a flame retardant.
 23. The precursor material ofclaim 22, wherein said particulate filler is selected from the groupconsisting of silica, alumina, silicates, talc, aluminosilicates, bariumsulfate, mica, diatomite, calcium carbonate, calcium sulfate, carbon,wollastonite, and combinations thereof.
 24. The precursor material ofclaim 23, wherein said particulate filler is surface-modified with acompound selected from the group consisting of fatty acids, silanes,alkylsilanes, fluoroalkylsilanes, silicones, alkyl phosphonates, alkylphosphonic acids, alkyl carboxylates, alkyldisilazanes, and combinationsthereof.